Preheat oven to 350 degrees.,In the bowl of an electric stand mixer fitted with the whisk attachment, beat egg whites until foamy.,Add vinegar and salt and beat on medium-high to soft peaks.,Slowly add sugar, about a tablespoon at a time, beating on high until whites are stiff and shiny.,Add vanilla then sprinkle cornstarch over whites and beat until incorporated.,On a parchment paper-lined baking sheet, pipe or spoon meringue into a 10-inch circle, making sides higher than the center.,Place in oven and turn heat down immediately to 300 degrees.,Bake 45 minutes and then turn oven off, leaving meringue in for an additional 40 minutes, or until crisp.,______,When completely cooled, remove meringue by gently peeling it off the parchment or by sliding an offset spatula or knife underneath the shell.